Robber control for electroplating



April 8, 1969 N. R. 61885 ETAL 3,437,578

ROBBER CONTROL FOR ELECTROPLATING Filed May 15, 1965 HI. HIH l1. 24

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INVENTORS JOSEPH R. HER/W656 NORMA/V R. GIBBS BY W "- ORNEYS U.S. Cl. 204-231 Claims ABSTRACT OF THE DISCLOSURE An electroplating apparatus having an element located between the anode and cathode for controlling the thickness of the material deposited on the cathode.

This invention relates generally to the art of electrolytic processing and in particular is directed toward controlling the degree of electrolytic processing of metal in order to produce a smooth variation over an area of the metalllc article which is being subjected to the electrolytic process.

Electrolytic processes such as electroplating and electrolytic etching are old and well known and the various steps and the reactions which take place in these processes are common knowledge. These processes are used for a variety of purposes. For example, electroplating and electrolytic etching are used to enhance the appearance of an article or to produce precision metallic circuits or to produce complex precision circuits out of metallic materials which do not readily lend themselves to other processes, etc. In some instances it is desired to control the degree of electrolytic reaction at least over a specified area of the article being processed. For example, electroplating has been used successfully for a period of time to build up or strengthen very fine precision metallic mesh or screen. For some applications it has been found desirable or necessary to have the plated area thicker over some portions than it is over others with a gradual variation in between.

It is a general object of this invention to provide means for controlling an electrolytic process so that the degree of electrolytic action varies over a selected area of the article being processed.

A more specific object of this invention is to achieve the immediately foregoing object in which the variation is uniform and gradual over the selected area.

Still another object of this invention is to achieve the foregoing objects in a relatively inexpensive manner.

Still another object of this invention is to achieve he foregoing objects wherein the location and degree of variation is selectively adjustable.

The present invention will be described as it is used to control electroplating of nickel onto a very fine wire screen or mesh. It will become apparent during the course of the following detailed description that although the invention is particularly useful for this purpose, it may be used for other applications with the accompanying advantages and features. Mesh which is plated to a variable thickness is commonly referred to as variation mesh. Obviously, the light transmission through the variation mesh will be inversely proportional to the degree of plating.

It is a further object of this invention to provide means for producing very fine mesh which has, over a preselected area, a smooth or gradual variation of the light transmission characteristics through the mesh.

A more specific further object of this invention is to provide means for producing variation metallic mesh hav- 3,437,578 Patented Apr. 8, 1969 ing gradual uniformly decreasing light transmission characteristics from the center of a prescribed area radially outward toward the edge of the area.

These and other objects and features of this invention will become apparent from the following detailed description with reference to the accompanying drawings in which:

FIG. 1 is a vertical sectional view of apparatus incorporating an embodiment of the invention;

FIG. 2 is a top view of the same apparatus illustrated in FIG. 1.

Referring now to the drawings, a suitable container 10 made of a non-conducting material contains an electrolyte which is suitable for the intended purpose. When used in the manner to be described for plating nickel on a copper screen an electrolyte which is commonly referred to as Watts bath is normally used. The composition of the bath does not constitute part of the invention and in general is well known to those of ordinary skill in the art of electrolytic processing. A holding fixture or rack 12, which is constructed of material which is non-conductive and does not react with the electrolyte, rests on the bottom of the container 10. The rack 12 contains a plurality of parallel vertical pairs of slots 13 along the inner facing surfaces of its side walls. These slots are spaced apart from one another along the side walls so as to provide means for locating various elements of the electroplating apparatus which may have to be spaced selectively at different distances from one another in a manner to be described shortly in greater detail.

Starting at what might be considered the front of the container 10 and mounted within one of the pairs of slots 13 in rack 12 is the member which constitutes the cathode 14 of the electroplating apparatus. The cathode 14 comprises a planar copper frame 15 which surrounds a very fine copper screen or mesh 16. The principal purpose of the frame 15 is to support the mesh 16 while it is being subjected to various processing steps and, in this process, to provide for making good electrical connection throughout the mesh. The method of initially producing the mesh 16 within its supporting frame 15 is not considered part of the instant invention and will not be described herein.

Rearward of the cathode 14 is a disc-shaped robber element 17. Although the size and shape of the robber element 17 is a matter of choice and depends on many factors including the desired extent and degree of control of the electroplating, in the instant illustrative embodiment the robber is made up of three separate discs 17a, 17b and 17c. The discs are of successively increasing diameters away from the cathode 14 and are rigidly connected together concentrically. All of the discs are made of electrically conductive material. The disc elements 17 are rigidly attached to the end of an elongated slender rod 18 which extends from behind and between the two elements 19 and 20 which constitute the anode. Rod 18, in turn, is supported by a non-conductive member 21 which extends downward into the container 10 from above. The support member 21 can be raised and lowered as desired to permit locating of the robber 17 in the desired vertical position. The robber can similarly be positioned laterally as desired, but, of course, this entails repositioning of the anode eleemnts 19 and 20 which are in the illustrated construction.

Just beyond the robber 17 are the previously referred to anode elements 19 and 20. These are elongated bars having at least an outer coating of nickel which is to be 3 deposited on the cathode 14. Although that surface of the anode elements which faces the cathode 14 has a curvature to it, it in effect forms a planar surface which is substantially parallel to the cathode 14 so that the normal electrolytic action between the two is in a straight line fashion.

The anode elements 19 and 20 are supported by hooks 22 which hang downward from a metal bar 23 which rests horizontally across the top of the container 10. By a suitable electrical conductor, the bar 23 is connected to the positive polarity output of a DC power source, not shown. Similarly, the cathode 14 is electrically connected to the negative polarity output of the same DC power source through suitable electrical connections which run from the frame up to a bus bar 24 which in turn is connected to the negative side of the power source. A suitable wire conductor 25, which may be arranged in any convenient manner electrically connects the robber 17 to the same DC energy level as the cathode 14. lit is understood, of course, that the anode elements, the cathode and robber are all immersed in the electrolytic bath within the container.

Between the robber 17 and the cathode 14, a fiat mask 26 is held in another pair of the slots 13 in the rack 12. The mask is rectangular in shape and is made with nonconductive material, such as clear plastic, and effectively constitutes an outer frame which defines an inner rectangular aperture 26a. The frame is somewhat wider than the frame 15 of the cathode and, therefore, overlaps it to a degree. However, the area of the aperture 26a is substantially greater than the area defined by the largest of the disk elements in robber 17.

In the practice of this invention the various elements are inserted into the bath-filled container 10 in their respective locations as described above. As pointed out earlier, the selection of the locations depends upon the desired degree and extent of control of the electroplating deposit. Typically, the robber 17 is centered with respect to the mesh 16 of the cathode 14 and the distance between the plane of the front face of the anode elements 19 and and the plane of the nearest disc in the robber 17 may be in the order of two inches and another two inches separates the robber from the cathode. The outer diameter of the robber 17 may be in the order of 4 /2 inches and the mesh portion of the cathode 14 may typically be in the order of 5 /2 inches square. With the anode elements 19 and 20, the cathode 14 and the robber 17 suitably connected to the respective output terminals. of an energized DC power source (not shown), electrolytic action through the bath will cause nickel to be released from the anode elements and carried toward the cathode 14. The effect of the robber 17 is to deprive the cathode of some of the nickel and cause it to deposit upon the robber instead of on the cathode. The size, shape, location, etc. of the robber with respect to the cathode will, of course, determine the degree and extent of the material which is robbed by the robber from the cathode and will determine the degree of variation in the mesh. In a typical case, where it was desired to have a 4% difference in the light transmission between the general center of the mesh and the outer edge, the DC power source was run at an output of 15 amperes for approximately 5 minutes. There resulted a mesh containing measured light transmission in the order of 41 /2 at the general center and approximately 37 /2% at the outer edge of the mesh with a relatively smooth variation therebetween. The mask 26 masks off the outer frame 15 of the cathode 14 to limit the amount of nickel that is deposited thereon since, as previously stated, the frame does not actually constitute a usable part of the mesh so nickel deposited thereon is Wasted. It can be visualized that the further the cathode is removed from the robber 17 the greater extent will be the area over which the robber will control the deposit (within practical limitations, of course) but the degree of variation from the center outward will be less. Conversely, of course, the closer the cathode is to the robber the smaller is the area which will be affected but a greater degree of variation will be produced in the electroplated mesh.

We claim:

1. For use in electroplating, in combination: an anode for providing a source of depositant and a cathode for providing a depository for the depositant, said anode and cathode having facing, substantially planar surfaces in spaced apart relationship adapted to be immersed in a suitable electrolyte; a plurality of electrically conductive planar disc-like elements having successively decreasing diameters mounted concentrically and spaced one behind the other with the largest disc being closest to the anode, said element adapted to be immersed within said electrolyte between said facing surfaces and electrically connected to said cathode, said elements receiving some of the depositant from said anode which otherwise would be deposited on the cathode, thereby producing a circular planar area on said cathode wherein the amount of depositant deposited thereon is gradually reduced radially inward.

2. Electroforming apparatus comprising: a container for holding a suitable liquid electrolyte; a rack constructed of nonconductive material resting within said container in the electrolyte, said rack containing a plurality of sets of vertical slots on the inner side of its side walls for supporting a substantially planar first electrode mounted within one of said sets of slots in a substantially vertical plane when immersed in said electrolyte and for supporting a second electrode having a substantially planar surface; a support bar mounted across at least part of said container above the level of the electrolyte; means for supporting said second electrode to said support bar with its planar surface immersed in the electrolyte and substantially parallel to said first electrode; means for making electrical connections to the respective electrodes; an electrically conductive disc-like member electrically connected to one of said electrodes and located within the electrolyte between said electrodes for at least partly controlling the electrolytic action between the electrodes over an area defined by said disc-like member; and means for adjusting the position of said disc-like member whereby the degree and location of the control of the electrolytic action can be varied.

3. The apparatus as described in claim 2 further including: a substantially planar non-conductive mask mounted within another of said sets of rack slots parallel to and located between said electrodes for further controlling the electrolytic action between said electrodes, said mask containing an aperture substantially greater in area than that defined by said disc-like member and positioned such that the aperture area encompasses the area defined by said disc-like member.

4. The apparatus as described in claim 3 wherein said disc-like member comprises plural concentric discs held in parallel, spaced relationship and electrically connected together.

5. Apparatus for use in electroplating a fine metallic mesh mounted within a surrounding electrically conductive planar frame, in combination: a container for holding a suitable liquid electrolyte; a rack within said container for holding the electrically conductive frame containing the metallic mesh in a vertical plane while immersed in the electrolyte; means for electrically connecting said frame to the negatively polarized side of an electrical energy source; an anodic source of material to be electroplated onto the mesh immersed in the electrolyte having a substantially planar face parallel to said frame; means for electrically connecting said anode to the positive polarity side of said electrical energy source; and a set of electrically conductive discs mounted concentrically in spaced relationship parallel to and located between said anode and the mesh within said frame While immersed in the electrolyte, said discs being successively smaller in diameter going away from the anode and being electrically 5 6 connected to said frame, whereby the degree of electro- FOREIGN PATENTS plating on said mesh is gradually greater radially outward 456,840 3/1928 Germany from the center of an area defined generally by the largest 697,747 9/1953 Great Britain of said dISCS.

References Cfled 5 JOHN H. MACK, Primary Examiner. UNITED STATES PATENTS DONALD R. VALENTINE, Assistant Examiner.

1,526,644 2/1925 Pinney 204-231 2,675,348 4/1954 Greenspan US. Cl. X.R.

2,831,808 4/1958 Esseff et al. 204297 297 2,936,270 5/1960 Webster et al. 204297 XR 10 3,039,951 6/1962 Clenard et al. 204297 

